ESD is the transfer of electrostatic charge between two objects. It is a rapid event that usually results when two objects of different potentials come into contact with each other. ESD may also occur when a high electrostatic field develops between two objects in close proximity. ESD has been known to cause device failures in the semiconductor industry.
There are several industry-standard ESD models that define how semiconductor devices are tested for ESD sensitivity under different situations of electrostatic build-up and discharge. For example, the human body model (HBM) simulates the ESD phenomenon where a charged body directly transfers its accumulated electrostatic charge to an ESD-sensitive device. The machine module (MM) simulates a more rapid and severe electrostatic discharge from a charged machine, fixture, or tool to the ESD-sensitive device at a lower potential. The charged device model (CDM) simulates a transfer of accumulated electrostatic charge from a charged device to another body of lower potential.
In the past, ESD protection devices for polysilicon fuses utilized soft grounded PMOS structures connected in series with a power supply to the polysilicon fuse. These ESD protection devices relied on the programming time of the polysilicon fuse to protect inadvertent programming of the fuse. Since an ESD event occurs for only a short duration, the 100 micro seconds programming time requirement for 90 nm transistors was typically long enough to prevent the polysilicon fuse to be inadvertently programmed by the ESD event.